Use bundle exec for kpeg dependencies

Author: hsbt

.github/workflows/gh-pages.yml

@@ -30,7 +30,7 @@ jobs:
         uses: actions/configure-pages@v3
       - name: Build with RDoc
         # Outputs to the './_site' directory by default
-        run: rake rdoc
+        run: bundle exec rake rdoc
       - name: Upload artifact
         uses: actions/upload-pages-artifact@v1